Devices communicating in a wireless local area network (WLAN) communicate data in packet form. A packet typically includes a header and the data to be sent and received. The header identifies the packet and the header contents are defined by the communication protocol used in the LAN. If the WLAN supports the IEEE standard 802.11 family of protocols (e.g., IEEE 802.11a-1999 (published Sep. 16, 1999), IEEE 802.11b-1999 (published Sep. 16, 1999), IEEE 802.11e-2005 (published Sep. 22, 2005), IEEE 802.11g-2003 (published Jun. 12, 2003), and IEEE 802.11n (yet to be formally published)), a device that communicates using the WLAN consists of two layers of functionality; a physical layer that transfers and receives bits of data wirelessly, and a media access control (MAC) layer that interfaces with the physical layer and, among other things, formats data into frames for transmission and deals with access to the WLAN. Frames can be transmitted to send data from one device to another and to acknowledge that a frame of data was sent correctly.
Protocol overhead refers to the amount of additional information needed to send a packet over a LAN in addition to the actual desired data. This includes a packet preamble to identify a signal as a packet, a packet header, and an acknowledge packet to indicate that the transmission was successful or need to be resent. Protocol overhead often prevents a WLAN from reaching achievable throughput.